Specific codec for a VoIP call

[vfonseca76]

Hi everyone

Some insight for my problem first:
A client has an IP500 R6.1, previously connected to a PRI trunk. Everything was working great, but he decided to change to SIP, due to excessive line failures and downtime on the PRI trunk.

The provider instaled a fiber ethernet access with Cisco routers, and provided an internet access and a SIP trunk on the same line.
So far, so good.

The VoIP calls are using G.729 and are working fine. The fax machine is working fine too, since the IP500 sends a reinvite and changes to T38.

The problem is an analog modem, used to connect to an old service still in use... it seems the darn thing wont work in T38.

I can always change the codec for the trunk, in sure the bandwidth will hold, but the increase in local traffic can cause some voice quality issues, despite the QoS configured on the switch's.

My question is: is there a way to specify the codec for a given call ? Can I force a call from that extn to use a specific codec, being a analog extension ?
By the way, this modem only MAKES the call, never receives.

Thank's in advance for you time.
Vasco

 

[amriddle01]

Modems very rarely work well over SIP if at all, faxes work as they use much lower bitrates, you may need to explore other avenues

 

[hairlessupportmonkey]

How about turn T.38 off and set your trunks to G.711 - might stand a chance of working then?

ACSS - SME
General Geek

 

[mforrence]

You'll need G.711 and low speed expectations for a modem to work across SIP. If this will be a "forever" thing, just get a POTS line from the local carrier and make the problem go away.